Selected poly(oxyalkylated) 1,3,4-thiadiazoles in acid baths and their use as corrosion inhibitors

ABSTRACT

Disclosed are selected poly(oxyalkylated) 1,3,4-thiadiazoles of the formula: ##STR1## wherein each R is individually selected from hydrogen and methyl; and the sum of y and z is from 2 to about 30. These compounds are shown to be effective corrosion inhibitors in corrosive liquids such as acid metal-treating baths.

This is a division of application Ser. No. 205,556, filed Nov. 10, 1980, now U.S. Pat. No. 4,329,475.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to selected poly(oxyalkylated) 1,3,4-thiadiazoles and their use as corrosion inhibitors.

2. Description of the Prior Art

The prior art has disclosed a wide variety of chemical compounds which effectively reduce the corrosive properties of liquids such as acid metal-treating baths. These inhibitors are generally added to the corrosive liquids to protect the metals in contact with these liquids. Alternatively, such inhibitors may be applied first to the metal surface, either as is, or as a solution in some carrier liquid or paste.

While many of these corrosion inhibitors have been used successfully for many years, stricter toxicological and other environmental standards are restricting the use of some of the compounds (e.g., chromates and dichromates). Accordingly, there is a need in the art to develop new and effective corrosion inhibitors which do not pose these environmental problems.

BRIEF SUMMARY OF THE INVENTION

The present invention is directed to, as compositions of matter, poly(oxyalkylated) 2-amino-5-mercapto-1,3,4-thiadiazoles of the formula (I): ##STR2## wherein each R is individually selected from H and CH₃ ; and the sum of y and z is from 2 to about 30.

The present invention is also directed toward the use of these compounds as corrosion inhibitors, particularly in acid metal-treating baths.

DETAILED DESCRIPTION

The poly(oxyalkylated) adducts of 2-amino-5-mercapto-1,3,4-thiadiazole may be made by reacting 2-amino-5-mercapto-1,3,4-thiadiazole with two or more moles of either ethylene oxide, propylene oxide, or mixtures thereof [either sequentially or mixed together]. The general reaction for making these adducts is illustrated by the following Equation (A) wherein 2-amino-5-mercapto-1,3,4-thiadiazole (AMTD) is reacted with 10 moles of ethylene oxide to produce the desired 2-amino-5-mercapto-1,3,4-thiadiazole.10 mole adduct product: ##STR3##

The 2-amino-5-mercapto-1,3,4-thiadiazole reactant may be made by the reaction of thiosemicarbazide with carbon disulfide (see French Pat. No. 1,064,234, which issued to Horclois et al. on May 12, 1954).

The ethylene oxide (EO) and propylene oxide (PO) reactants are commercially available chemicals which may be obtained from many sources. Mixtures of EO and PO may be employed as reactants, either added sequentially or mixed together.

It should be understood that the number of moles of EO or PO reacted at each of the two reactive sites of the 2-amino-5-mercapto-1,3,4-thiadiazole molecule will not necessarily always be the same. For instance, as shown in Equation (A), above, (where 10 moles of EO were reacted), it does not necessarily follow that 5 moles of EO will react at the 5-mercapto site and 5 moles of EO will react at the 2-amino site. Instead, it may be likely that in some instances only 2 moles, or more or less, may react at the 5-mercapto site and may be 8 moles, or more or less, may react at the 2-amino site. Furthermore, it should be understood that the total number of EO or PO moles on each resulting adduct molecule will be a statistical distribution. Thus, the sum of y and z in Formula (I) represents the average number of EO or PO units per adduct and that the actual number on any given adduct may be less or greater than the sum. That is, when y+z=10, it is meant that ten moles of EO or PO have been reacted per mole of the 1,3,4-thiadiazole. Preferably, it is desired to employ from about 5 to about 20 moles of EO or PO per one mole of the desired 1,3,4-thiadiazole. More preferably, it is desired to use from about 5 to about 10 moles per mole of the desired 1,3,4-thiadiazole.

Any conventional reaction conditions designed to produce these poly(oxyalkylated) 1,3,4-thiadiazole adducts may be employed in the synthesis of the present compounds and the present invention is not intended to be limited to any particular reaction conditions. Advantageously and preferably, the present compounds may be made according to the reaction illustrated by Equation (A) in the presence of an inert solvent such as dioxane and dimethyl formamide (DMF) and an alkaline catalyst like potassium hydroxide or sodium methylate. However, the use of a solvent and a catalyst is only desirable, and not necessary. The reaction temperature and time will both depend upon many factors including the specific reactants and apparatus employed. In most situations, reaction temperatures from about 80° C. to about 140° C., preferably from about 85° C. to about 110° C. may be employed. Reaction times from about 30 minutes to about 600 minutes may be employed. The reaction may preferably be carried out at atmospheric pressure or under pressure from about 10 to about 100 psig or more, if desired. The desired adduct product may be recovered from the reaction mixture by any conventional means, for example, evaporation of the solvent, filtration, extraction, recrystallization or the like.

It should be noted that while the reaction illustrated in Equation (A) is the preferred method for preparing the compounds of the present invention, other synthetic methods may also be employed.

Also, in accordance with the present invention, it has been found that the compounds of Formula (I), above, may be utilized as effective corrosion inhibitors. In practicing the process of the present invention, metal surfaces are contacted with an effective corrosion-inhibiting amount of one or more of these compounds. "Metal surfaces" which may be protected by the corrosion-inhibition properties of the compounds of the present invention include ferrous and non-ferrous metals such as cast iron, steel, brass, copper, solder, aluminum, and other materials commonly used with corrosive liquids. It is understood that the term "effective corrosion-inhibiting amount" as used in the specification and claims herein is intended to include any amount that will prevent or control the corrosion on said metal surfaces. Of course, this amount may be constantly changing because of the possible variations in many parameters. Some of these parameters may include the specific corrosive material present; the specific compound used; the specific metal to be protected against corrosion; the salt and oxygen content in the system; the geometry and capacity of the system to be protected against corrosion; flow velocity of the corrosive material; temperature and the like.

One preferred use of the corrosion inhibitors of the present invention is in aqueous acidic solutions or baths which are in contact with metal surfaces. Such acidic solutions include mineral acid solutions such as sulfuric acid, hydrochloric acid, or the like. These acidic solutions may be used for acid-pickling baths for the surface cleaning of metals or in similar processes. The preferred amount of this corrosion inhibitor in such acid solutions is preferably at least 0.005% by weight of the solution; more preferably, from about 0.01% to about 0.5% by weight of the solution or bath.

Acid pickling solutions or baths are commonly used to remove rust or scale from the surfaces of metals. In commercial operations, this rust or scale is removed by immersing a metal sheet, plate, bar, or the like in the acid pickling solution. The acid solution attacks and dissolves the rust or scale. Once the scale is dissolved, the acid is then free to further attack the metal surface. In order to reduce this attack on the metal, corrosion inhibitors are added to the pickling acid solution.

The compounds of this invention may be used for other corrosion protection applications beside the above-mentioned preferred applications. In addition, these compounds may be employed with other known corrosion inhibitors and/or with inert substances such as fillers, dispersing agents, and the like.

The following examples further illustrate the present invention. All parts and percentages employed herein are by weight unless otherwise indicated.

EXAMPLE 1 2-Amino-5-mercapto-1,3,4-thiadiazole.3 ethylene oxide

2-Amino-5-mercapto-1,3,4-thiadiazole [13.3 g (0.1 mole)] was placed in 100 ml of DMF with 0.2 g of NaOH and heated to 80°-100° C. Ethylene oxide [69.6 g (1.6 moles)] was slowly dropped in over three hours. The mixture was cooled and the solvent and unreacted EO removed under vacuum to give 30 g of orange liquid with an elemental analysis as follows:

    ______________________________________                                                    C    H          N      S                                            ______________________________________                                         Calculated for                                                                 AMTD.3EO:    36.23  5.70       15.84                                                                               24.23                                      Found:       36.90  5.91       15.81                                                                               19.43                                      ______________________________________                                    

EXAMPLE 2 2-Amino-5-mercapto-1,3,4-thiadiazole.8 ethylene oxide

2-Amino-5-mercapto-1,3,4-thiadiazole [53.2 g (0.4 moles)], KOH (3.4 g) and DMF (300 ml) were charged in a pressure vessel. After purging with N₂, it was heated at 95°-100° C. while adding [176 g (4 moles)] of EO over one hour. The mixture was post-reacted 3 hours at 100° C. Removal of the solvent and unreacted EO in vacuo left 194.6 g of viscous brown liquid with an elemental analysis as follows:

    ______________________________________                                                    C    H          N      S                                            ______________________________________                                         Calculated for                                                                 AMTD.8EO:    44.67  7.09       8.68 13.22                                      Found:       42.85  7.16       8.57 10.41                                      ______________________________________                                    

EXAMPLE 3

Stock solutions of the inhibitors were made by weighing 10 grams of the test compound into a 100 ml volumetric flask and filling with either ethanol or dimethylformamide to give a 10% weight/volume concentrate. This concentrate was pipetted into weighed 500 ml flasks and acid added to give 500 g of solution of required inhibitor concentration.

Coupons measuring about 76 mm×18 mm×1.5 mm made from 1010 steel were sanded with 240 grit paper, degreased in acetone and weighed after drying. After the tests, the coupons were scrubbed with pumice, rinsed with water, acetone and re-weighed after drying. All runs were made in duplicate and average values reported. The tests were run in glass flasks and the coupons were suspended from glass rods, two per flask.

The tests at ambient temperature (75° F.±3° F.) were run for 24 hours in 10% hydrochloric acid and in 20% sulfuric acid. The high temperature tests, 190° F.±1° F., were run for three hours in 10% hydrochloric acid and in 5% sulfuric acid.

In Tables 1-4, below, the corrosion rate (in mills per year--MPY) and the percent inhibition (%I) are given. These results were determined by the following formulae: ##EQU1##

The symbols used in the Tables stand for:

AMTD=2-amino-5-mercapto-1,3,4-thiadiazole

EO=ethylene oxide

The above equation for MPY may be found in NACE Standard Test Method 01-69: "Laboratory Corrosion Testing of Metals for the Process Industries."

As can be seen from the results in these Tables, the corrosion inhibitors of the present invention that were tested are all effective corrosion inhibitors in aqueous acidic solutions.

                  TABLE 1                                                          ______________________________________                                         CORROSION RATE IN MPY IN 10% HCl AT 75° F.                              Compound    1000 ppm (% I)     500 ppm                                                                               (% I)                                    ______________________________________                                         Blank       463                463                                             AMTD.3EO    29.4     (93.7)    28.2   (93.9)                                   AMTD.8EO    28.6     (93.8)    26.0   (94.4)                                   ______________________________________                                    

                  TABLE 2                                                          ______________________________________                                         CORROSION RATE IN MPY IN 20% H.sub.2 SO.sub.4 AT 75° F.                 Compound    500 ppm  (% I)     250 ppm                                                                               (% I)                                    ______________________________________                                         Blank       241.5                                                              AMTD.3EO    15.7     (93.5)    13.8   (94.3)                                   AMTD.8EO    12.9     (94.7)    11.8   (95.1)                                   ______________________________________                                    

                  TABLE 3                                                          ______________________________________                                         CORROSION RATE IN MPY IN 10% HCl AT 190° F.                             Compound         1000 ppm (% I)                                                ______________________________________                                         Blank            57,982                                                        AMTD.3EO         3,637    (93.7)                                               AMTD.8EO         5,310    (90.8)                                               ______________________________________                                    

                  TABLE 4                                                          ______________________________________                                         CORROSION RATE IN MPY IN 5% H.sub.2 SO.sub.4 AT 190° F.                 Compound         1000 ppm (% I)                                                ______________________________________                                         Blank            14,079                                                        AMTD.3EO         450      (96.8)                                               AMTD.8EO         737      (94.8)                                               ______________________________________                                     

What is claimed is:
 1. An acid metal-treating bath comprising an acid and an effective corrosion-inhibiting amount of a poly(oxyalkylated) 1,3,4-thiadiazole having a formula: ##STR4## wherein each R is individually selected from either H or CH₃ ; and the sum of y and z is from 2 to about
 30. 2. The acid bath of claim 1 wherein the acid comprises sulfuric acid or hydrochloric acid.
 3. A process for inhibiting corrosion of metal surfaces caused by corrosive aqueous solutions, which comprisescontacting said metal with an effective corrosion-inhibiting amount of a poly(oxyalkylated) 1,3,4-thiadiazole having a formula: ##STR5## wherein each R is individually selected from either H or CH₃ ; and the sum of y and z is from 2 to about
 30. 4. The process of claim 3 wherein each R is H.
 5. The process of claim 3 wherein each R is CH₃.
 6. The process of claim 3 wherein at least one R is H and at least one R is CH₃.
 7. The process of claim 3 wherein the sum of y and z is from about 5 to about
 20. 8. A process of inhibiting the corrosion of metals which come into contact with an acid solution, which comprises contacting the surface of the metal to be inhibited against corrosion with the corrosion-inhibited acid metal-treating bath of claim
 1. 9. The process of claim 8 wherein the acid in acid bath comprises sulfuric acid or hydrochloric acid. 